The present invention relates to flow control valves of the quarter-turn ball valve type, and more particularly, to ball valve assemblies used in isolating electronic level transmitters operatively connected to fluid storage tanks.
Electronic liquid level transmitters are utilized extensively with fluid storage tanks in the chemical and pulp and paper industries to monitor the volume of fluid contained in a tank. Liquid level transmitters have diaphragm faces that are placed in fluid communication with the bottom of a fluid storage tank, which measure the head pressure caused by changes in the liquid level and transmit an electronic output signal proportional to the measured head pressure. The output signal produced by an electronic level transmitter is then used to monitor the liquid level and volume in the storage tank or the density of the material stored in the tank where the volume of material in the tank has been determined by another means. In many manufacturing environments, level transmitters provide a continuous level indication that is one of several variables monitored in a complex process control system. For such systems, maintaining the level transmitter in proper working order is critical to maintaining safe and normal process operations. Reliable and accurate electronic level transmitters are relied upon to avoid hazardous and costly operational upsets, such as tank overflows.
Electronic level transmitters are typically of the flange-mounted type, which connect to outlet piping located at or near the bottom of a fluid storage tank. In many cases, liquid storage tanks are provided at the bottom with a three inch pipe and flanged outlet for attaching the level transmitter. Such flange-mounted transmitters are therefore typically sized for use with three inch outlet piping, and a three inch, class 150 ANSI pipe size flange connector. The level transmitter may be provided with a diaphragm face for sensing the liquid head pressure that is flush mounted to the flange, that is, a planar diaphragm face mounted flush with gasket surface of a three inch, class 150 ANSI flange.
A transmitter isolation valve is required between the tank outlet piping and the level transmitter to allow the transmitter to be removed without having to drain the tank or otherwise disrupt process operations, such as for repairs, cleaning, re-calibrating or replacement of the transmitter. One of the largest users of level transmitters is the pulp and paper industry, and it is well known in the prior art to utilize three-inch sized knife gate valves for transmitter isolation. For this application, level transmitters of the knife gate type have the benefit of being narrow-body, which allows the isolation valve to be mounted as close to the liquid storage tank as possible. This saves valuable space in crowded manufacturing environments and provides for greater access to the transmitter for maintenance workers and equipment. Additionally, storage tanks in the pulp and paper industry are often used to store aqueous liquids that contain varying degrees of sedimentation and pulp fibers that settle at the bottom of storage tanks. Level transmitters mounted closely to a storage tank eliminate excess piping space for the buildup of sediment and pulp fibers.
But there are many limitations associated with the use of transmitter isolation valves of the knife gate type. For instance, because these valves are mounted close to the storage tanks to which they are operatively connected, there is not enough room to utilize a typical round handwheel to open and close the valve. To open and close such valves, operators are required to rely on a ratchet-type device with a piece of pipe, or ratchet wrench, as a handle. This requires an excessive number of strokes of the handle to open and close the valve. On account of the corrosive nature of the fluids utilized with these valves, another limitation is the valves often corrode and fail to function effectively. An additional limitation of knife gate valves is difficulty associated with preventing leakage through the gate seat area because the valve stays open for long periods of time.
Additional difficulties associated with the use of knife gate transmitter isolation valves pertain to the manner in which the gate, or blade, of the valve must be sealed as it extends and retracts through the packing gland during use. Because of the wide, flat, and thin dimensions of typical blades, as well as the blades having four sharp and square corners, the pressing of the packing material against the blade to prevent leakage from the valve into the atmosphere can be problematic. For instance, tightening the packing gland of such valves can render the valve inoperable due to excessive levels of force being required to move the blade up or down. Loosening the packing gland to allow the valve to readily open and close may result in the problem of external leakage. As the result of increasingly stringent leak prevention performance standards for industrial valves issued by such agencies as the Environmental Protection Agency (EPA) and Occupational Health and Safety Administration (OSHA), these problems have become more significant and costly.
On account of the limitations of knife gate valves for use in isolating level transmitters, valves of the ball valve type have begun being used in this service. These valves are quarter-turn valves wherein an internally mounted ball member rotates between a ninety degree arc to open or close the valve. These valves are typically teflon-seated to allow for leak-tight shutoff and are manufactured of stainless steel, hastelloy, or titanium for corrosion resistance. There has been a reluctance to accept valves of the ball valve type as a suitable replacement for knife gate valves. One reason is in order to be a direct replacement for narrow knife gate valves, conventional ball valves for use in isolating transmitters have had narrow flow-through ports in conjunction with a recess machined into the transmitter side of the valve body to provide a three inch sensing area for the diaphragm of the level transmitter. Narrow flow-through ports increase the likelihood that the isolation valve will be plugged by sedimentation and pulp fibers, creating operating problems. Further, there is a need to provide conventional transmitter isolation valves of the ball valve type with improved backflushing means, which would reduce the need for costly removal of the level transmitter for maintenance or replacement of the level transmitter.
From the foregoing it may be seen that heretofore, no one has adequately provided a ball valve for use in isolating level transmitters. A need exists for a corrosion resistant, quarter-turn ball valve for use in isolating a level transmitter that provides bubble-tight shutoff, that may be easily installed as a replacement for knife gate or other flanged valves and that addresses the limitations of the prior art transmitter isolation valves of the knife gate and ball valve type.
It is an object of the present invention to provide an improved ball valve which is superior to those presently used to isolate electronic level transmitters.
A further object of the present invention is to provide a transmitter isolation ball valve that provides means for flushing the diaphragm face of an electronic level transmitter operatively connected thereto.
Another object of the present invention is to provide a transmitter isolation ball valve having a full port for enhancing the accuracy of level transmitter readings and the backflush capabilities of the valve.
A still further object of the present invention is to provide a transmitter isolation ball valve that may be readily used for replacing transmitter isolation valves of the knife gate type.
Another object of the present invention is to provide a transmitter isolation valve having means for flushing the diaphragm face of a level transmitter when the valve is in an open position and means for calibrating the level transmitter when the valve is in a closed position.
A further object of the present invention is to provide a transmitter isolation valve having a single flush port for backflushing the diaphragm face of a level transmitter when the valve is in an open position and also for depressuring the valve body when the valve is in a closed position.
These and other objects of the present invention are accomplished through the use of a ball valve assembly of the quarter-turn type for use in isolating a level transmitter comprising a valve body having an inlet or tank-side port, an outlet or transmitter side port, an inner chamber, and a substantially spherical ball valve member mounted in the chamber for selective rotation between an open position and a closed position. When the ball valve member is in an open position, fluid communication is established between the inner chamber and the inlet port and outlet port to allow fluid flow therethrough.
The ball valve member of the present invention has an inner surface forming a substantially cylindrical through passage that is in axial alignment with the inlet port and outlet port to allow fluid flow therethrough when the ball valve member is in an open position. The present invention, unlike conventional transmitter isolation valves, preferably provides a full port that is a cylindrical opening through the ball valve assembly having a uniform diameter substantially identical to the nominal pipe size connected thereto. Overcoming the limitations of the prior art, a full port configuration minimizes interference on the operation of a level transmitter resulting from the presence of a restricted opening across the transmitter isolation valve and associated increased pressure drop across the valve. This allows the level transmitter to operate more accurately and with less maintenance. The present invention preferably has a cylindrical opening through the valve body having a minimum diameter equal to the nominal size of standard three-inch inner diameter tank side piping.
The present invention further preferably comprises means for flushing a flush-mounted diaphragm face of a level transmitter connected to the outlet port. The present invention comprises a purge port positioned on the valve body that is in alignment with a cylindrical purge passage formed in the ball valve member when the ball valve member is in an open position. The purge passage has a first end formed in the inner surface of the ball valve member and a second end formed in an outlet port sealing face of the ball valve member. The purge passage is located concentrically about a purge passage axis that passes through the outlet port when the ball valve member is in an open position. In this manner the purge port and purge passage provide means for directing a purge fluid onto the diaphragm face of a level transmitter operatively connected to the outlet port of the ball valve assembly. This provides means for flushing the diaphragm face of the level transmitter and means for backflushing the valve which is enhanced by the full port configuration of the valve. Thus, the present invention provides means for reverse flushing or backflushing the ball valve assembly without removing it from the piping on which it is installed or draining the storage tank and associated piping.
The purge passage further preferably provides means for depressuring the inner chamber of the valve body with the ball valve member moved to the closed position. This enhances safety associated with level transmitter maintenance, by relieving excess pressure buildup between the sealed inlet port and the level transmitter prior to removing the level transmitter from the outlet port. Depressuring the inner chamber of the ball valve body with the ball valve member in a closed position also provides confirmation that the inlet port is properly sealed prior to removing the level transmitter. In addition to bleeding off entrapped pressure, media collected in the valve body can also be removed prior to removing the level transmitter. Additionally, the purge passage and purge port also provide for calibration of the level transmitter without disrupting process operations, because fluid communication is established between the purge port and transmitter when the ball valve member is in the closed position. With the valve in a closed position, a pressure testing device can be attached to the purge port to calibrate the level transmitter. It can be appreciated that the single purge/calibration port of the present invention may be utilized to not only flush the diaphragm face of the level transmitter and backflush the ball valve assembly with the valve in an open position, but also to depressurize the ball valve assembly and calibrate the level transmitter with the valve in a closed position.
The present invention may also be utilized to readily replace transmitter isolation valves of the knife gate type. The valve assembly includes a pair of opposing flanges, a transmitter side flange and a tank side flange. The transmitter side flange is provided with four bolt holes positioned along the outer periphery of the flange in a standard ANSI 150 stud bolt orientation. The tank side flange of the present invention provides four bolt holes in this standard configuration, and additionally two upper bolt slots that accommodate nonstandard pipe flanges, namely, pipe flanges configured to mount an isolation valve of the knife gate type. This allows the present invention to replace a transmitter isolation valve of the knife gate type without having to replace or retrofit the pipe flange used in mounting the knife gate valve.
The present invention also overcomes limitations relating to the mounting of certain prior art transmitter isolation ball valves where a knife gate transmitter isolation valve had been used. Many of such valves required special cut-to-length all-threaded studs to mount the valve. Some models required that existing threaded bolt holes be drilled out to allow them to be slipped over the special threaded studs. Other models intended to eliminate this need causes the transmitter isolation valve and level transmitter to be positioned approximately twelve and one-half degrees from vertical when mounted. The present invention eliminates all of these undesirable mounting limitations. To mount the present invention in the desired vertical position where a knife gate transmitter isolation valve had been used requires only eight standard off-the-shelf hex head cap screws.
The present invention further preferably comprises means for selectively rotating the ball valve member comprising a handle with an upper flat portion with a longitudinal axis that is offset from the centerline of the valve body. The offset angle is preferably forty-five degrees, which allows the present invention to be utilized in a cavity formed in tank wall insulation where the ball valve assembly is installed in a recessed area within the tank wall installation. With the handle configuration of the present invention, the distal end of the handle will clear insulation as it is moved between an open and closed position, thereby minimizing the size of the cavity necessary to operate the ball valve assembly.
These and other objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiment of the invention.